// $Id: parser.js 94 2012-03-02 14:31:59Z www.todaysworld.in@gmail.com $ -->

// Copyright 2005 Nagarjuna Venna <vnagarjuna@yahoo.com>
// See http://lekhini.org/scripts/padma-license.txt

// See http://lekhini.org/license.txt

//Basic parser adequate for processing text encoded in Unicode, ISCII etc.
//This is the prototype for more specialized parsers
//Also includes the state machine

//Parser states
Parser.state_START  = 0;    //Syllable hunt starts from this state
Parser.state_CONSNT = 1;    //Found a consonant to start the syllable
Parser.state_PREFIX = 2;    //Found a prefix symbol
Parser.state_HALFORM = 3;   //Saw a half form

function Parser(input, encoding) {
	this.index = 0;
	this.length = input.length;
	this.text = input;
	this.state = Parser.state_START;
	this.cache = { key: null, value: null };
	this.encoding = encoding;
}

Parser.prototype.more = function ()
{
	return this.index < this.length;
}

Parser.prototype.next = function ()
{
	var response = new Syllable();

	var remaining = this.length - this.index;
	for(; remaining > 0; remaining = this.length - this.index) {
		var key = null, value = null;

		if (this.cache.key == null) {
			var maxLookupLen = remaining > this.encoding.maxLookupLen ? this.encoding.maxLookupLen : remaining;
			
			for(var i = maxLookupLen; i > 0; i--) {
				key = this.text.substring(this.index, this.index + i);
				//alert("looking up " + key);
				value = this.encoding.lookup(key);
				if (value != null) {
					//alert("found match " + value);
					break;
				}
			}
		}
		else {
			value = this.cache.value;
			key = this.cache.key;
			this.cache.key = this.cache.value = null;
		}

		this.handleInput(value, key, response);
		if (this.state == Parser.state_START)
			return response.getSyllable();
	}

	if (this.state == Parser.state_CONSNT)
		this.handleConsonantTermination(response);
	return response.getSyllable();
}

//Change symbol type based on state
//No need to change symbol type by default
Parser.prototype.updateSymbolType = function (type)
{
	return type;
}

//no op
Parser.prototype.handleConsonantTermination = function (current)
{
}

Parser.prototype.isCurrentSyllableComplete = function (type)
{
	return type == Padma.type_accu_mod || type == Padma.type_gunintam || type == Padma.type_hallu_mod;
}

//State Machine
//The parser has just determined that value is a match for key
//value is built into current 
Parser.prototype.handleInput = function (value, key, current)
{
	var old_type = Padma.type_unknown, symbol = value;
	if (symbol != null)
		old_type = Padma.getType(symbol.charAt(0));
	else symbol = key;

	var prefix = false, suffix = false;
	if (arguments.length >= 4)
		prefix = arguments[3];
	if (arguments.length >= 5)
		suffix = arguments[4];

	//alert("state = " + this.state + ", type = " + old_type + ", prefix = " + prefix + ", suffix = " + suffix);

	var type = this.updateSymbolType(old_type);
	if (type != old_type) {
		symbol = Padma.dependentForm(symbol);
		//alert("new type = " + type);
	}

	switch (this.state) {
		case Parser.state_START:
		case Parser.state_PREFIX: {
			this.index += key.length;
			current.update(symbol, type, prefix, suffix);
			if (prefix == true)
				this.state = Parser.state_PREFIX;
			else {
				if (type == Padma.type_accu || type == Padma.type_digit || type == Padma.type_unknown) {
					//Current syllable is complete
					this.state = Parser.state_START;
					//alert("1: syllable complete");
				}
				else if (type == Padma.type_hallu) {
					//Wait for more
					//alert("3: consonant start");
					this.state = Parser.state_CONSNT;
				}
				else if (type == Padma.type_half_form) {
					//alert("6: Half form");
					this.state = Parser.state_HALFORM;
				}
				else {
					//gunintalu, vattulu and vowel/consonant modifiers should not appear in isolation, accept it silently
					//alert("2: bad input");
					this.state = Parser.state_START;
				}
			}
			return;
		}

		case Parser.state_CONSNT:
		case Parser.state_HALFORM: {
			var nextTypes = Padma.type_accu | Padma.type_digit | Padma.type_unknown;
			if (this.state == Parser.state_CONSNT)
				nextTypes |= Padma.type_hallu | Padma.type_half_form;

			if (((type & nextTypes) || prefix) && !suffix) {
				//next syllable has started, process it again next time around.
				this.cache.key = key;
				this.cache.value = value;
				this.state = Parser.state_START;
				//alert("4: cache for next syllable");
				this.handleConsonantTermination(current);
				return;
			}

			if (this.state == Parser.state_HALFORM && type == Padma.type_hallu)
				this.state = Parser.state_CONSNT;
			this.index += key.length;
			if (this.isCurrentSyllableComplete(type)) {
				//Syllable is complete
				this.state = Parser.state_START;
				//alert("5: syllable complete");
			}
			current.update(symbol, type, prefix, suffix);
			return;
		}
	}
	//should never reach here
	//Figure out an assertion
	return;
}
